1. Field of the Invention
The present invention relates to alarm systems and more particularly to a device specifically designed to automatically disrupt power to an alarm system's siren when the alarm system is generating false alarms.
2. Description of Prior Art
Alarm systems are commonly used in automobiles, homes, and businesses. They are generally installed with the intention of discouraging break-ins by ensuring that a criminal's illegal act will be quickly detected and brought to the attention of property owners, neighbors, and/or authorities within the community.
Once an alarm system is triggered, or detects a break-in, it typically sounds an audible alert from a siren. Most alarm systems include a timer that automatically resets the triggered alarm system after a predetermined period of time, silencing the siren. Communities are often very sensitive to noise pollution, especially in high-density urban environments, and it is expected that alarm systems will only sound their sirens for a limited period of time.
False alarms, defined as the alarm system's siren sounding an audible alert when there is no actual break-in in progress, are an ongoing problem. Most prior art attempts to reduce the occurrence of false alarms by improving the reliability of the alarm system's sensors or by carefully analyzing data from sensors in an attempt to determine the legitimacy of the break-in detection. But in spite of these efforts false alarms are still common. So many factors contribute to false readings from sensors that it is difficult to ever completely eliminate false alarms. Such factors may include changes to temperature, humidity, moisture, pressure, background noise, or other environmental factors. Corrosion on contacts or connectors, lightning strikes, or component degradation within the system may cause a sensor or alarm system's processing unit to trigger an alarm. Improperly calibrated sensors or incorrect alarm installation, as well as other human error, may also contribute to false alarms.
Once the siren is activated, the alarm system relies on the timer to automatically reset the triggered alarm system after a predetermined period of time. But four types of commonly occurring false alarms have the potential of causing the alarm system's siren to sound for an extended, and unreasonable, amount of time, even if the reset timer is present. These false alarms force neighbors to endure loud noise pollution from the siren, as they have no recourse in silencing the siren other than calling the police, who may forcibly silence the offending siren. In many communities, a car owner with this type of malfunctioning alarm may have his car towed while homeowners may be faced with a fine for requiring police attendance. In either case, the false alarm has the potential of costing the alarm owner money.
Type-1 False Alarm and Prior Art Prevention
The first type of false alarm that causes extended sounding of the siren is referred to as a type-1 false alarm in this discussion. It is characterized by a malfunctioning sensor that repeatedly and continuously outputs a change of state, indicating a break-in detection. Once the alarm system has sounded its siren for a period of time and has automatically reset itself, this malfunctioning sensor will immediately cause the alarm system to be retriggered, resulting in the siren sounding once again. The alarm system's automatic reset does not prevent the false alarm and the extended sounding of the siren. This type of false alarm is commonly encountered in car alarms and home alarms that can be heard repeatedly sounding a siren for several minutes, going silent for a second, sounding the siren again for several minutes, then going silent for a second. The alarm system will continue this noise pollution until the owner returns to disarm the alarm system or the malfunctioning sensor stops sending repeated change of state signals.
Some alarm systems have processing units with more advanced sensor output comparison and analysis capabilities that have the ability to detect this type of malfunctioning sensor and ignore it, a feature known as automatic sensor bypass. Although this feature may help to prevent this type of false alarm, it is generally only found in very expensive alarm systems, as it requires special analysis of every sensor signal entering the alarm system's processing unit. Automatic sensor bypass also requires dedicated wiring to every sensor in the alarm system, rather than connecting sensors on common normally-open or normally closed wire loops. Finally, for existing alarm system owners the addition of automatic sensor bypass to reduce false alarms requires a complete upgrade of the alarm system, which is both expensive and time-consuming.
Type-2 False Alarm and Prior Art Prevention
The second type of false alarm that causes extended sounding of the siren, referred to as a type-2 false alarm in this discussion, is a malfunctioning alarm system's processing unit. Even though the processing unit may be carefully designed to run reliably, and may include an automatic alarm system reset circuit and automatic sensor bypass, it may still malfunction due to any number of environmental factors or functional failures. For example, the mechanical relay responsible for switching on the siren may fail or moisture may disrupt the proper function of the processing unit's electronics. It is possible for an alarm system's processing unit to enter into and remain in the triggered state. This type of failure results in the alarm system's siren turning on and indefinitely remaining steadily on.
Type-3 False Alarm and Prior Art Prevention
The third type of false alarm that causes extended sounding of the siren, referred to as a type-3 false alarm in this discussion, is a sensor that repeatedly yet intermittently indicates a change of state. This is similar to the type-1 false alarm described above, except in this case the sensor outputs a change of state to the processing unit intermittently rather than continuously. This type of false alarm is often due to an improperly calibrated sensor, such as a car alarm system's vibration sensor calibrated to be too sensitive. In this example, every time a truck drives by the vibration sensor, the alarm system enters the triggered state and the siren sounds.
This false alarm is very common and can be identified by the siren sounding for a period of time, such as several minutes, followed by an extended period of silence, such as 20 minutes, followed again by several minutes of the siren sounding. Environmental conditions can contribute to an improperly calibrated sensor that generated this type of false alarm. Other improper alarm installation procedures, such as accidentally aiming a motion detector outside where passersby cause the alarm to enter the triggered state, may also contribute to this type of false alarm. Even highly reliable sensors and the inclusion of an automatic alarm reset circuit and automatic sensor bypass don't prevent an alarm system from generating this type of false alarm.
Type 4 False Alarm and Prior Art Prevention
The fourth and final type of false alarm that causes extended sounding of the siren, referred to as a type-4 false alarm in this discussion, is alarm system user error. One very common form of this type of false alarm involves accidental arming of the motion detectors within a building when occupants are present. It is common for a home alarm system to include both perimeter sensors, such as window and door magnetic reed switches, and interior motion detectors. These two types of sensors can often be separately armed. The advantage to this capability is to permit movement within the house while still protecting the perimeter against break-ins.
However, consider a homeowner who accidentally arms both the perimeter and interior motion sensors of a home when a pet is in the house, then leaves the premises. The movements of the pet throughout the house will cause the alarm system to repeatedly yet intermittently enter the triggered state, and sound the alarm system's siren. For neighbors, the siren sounding characteristics of this type of false alarm are identical to those of the type-3 false alarm; the siren sounds repeatedly yet intermittently. Because type-3 and type-4 false alarms demonstrate the same siren sounding characteristics, these two types of false alarms are collectively referred to as a type-3/4 false alarm in this discussion. It is not uncommon for alarm system owners to learn, from neighbors, that their alarm system repeatedly sounded throughout the day or night because of the accidental triggering of motion sensors while a pet was left alone in the home. Once again, improved sensor reliability, the inclusion of an automatic alarm reset circuit, and automatic sensor bypass don't prevent an alarm system from generating this type of false alarm.
Summary
All four types of false alarms described above have the potential of causing the alarm system's siren to sound for extended periods of time. Even with the many improvements to sensor reliability, and the inclusion of an automatic alarm system reset circuit, these four types of false alarms are still common and unresolved. An otherwise reliable alarm system can one day unexpectedly generate any one of these types of false alarms. Alarm owners, conscious of disturbing neighbors or incurring fines for such false alarms, are discouraged from always arming their alarms when they aren't present. This leaves their property unprotected. Other users elect to eliminate the alarm's siren altogether and communicate an alarm system triggering to remote monitoring services via radio or telephone links. Without a siren, a criminal may not be scared away from property that the alarm system is designed to protect.